I have a double wide mobile home with existing slider and replacing it with french doors. The size is going from 71 1/2 x 76 to 71 1/2 x 80. I don't believe that there are cripple studs above the header, just a solid header.
My idea is to cut into the header a bit more than needed for the door to allow me to add a new plate under what is left of the header instead of replacing the header. Is that a sufficient fix? Should I not use wood but use a steel plate under the header?